On Mon, May 29, 2023 at 03:03:52PM +0200, Vlastimil Babka wrote:
> On 5/19/23 14:39, Johannes Weiner wrote:
> > The different branches for retry are unnecessarily complicated. There
> > are really only three outcomes: progress (retry n times), skipped
> > (retry if reclaim can help), failed (retry with higher priority).
> >
> > Rearrange the branches and the retry counter to make it simpler.
> >
> > v2:
> > - fix trace point build (Mel)
> > - fix max_retries logic for costly allocs (Huang)
> >
> > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> > ---
> > mm/page_alloc.c | 53 +++++++++++++++----------------------------------
> > 1 file changed, 16 insertions(+), 37 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 5a84a0bebc37..72660e924b95 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3772,16 +3772,22 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
> > * Compaction managed to coalesce some page blocks, but the
> > * allocation failed presumably due to a race. Retry some.
> > */
> > - if (compact_result == COMPACT_SUCCESS)
> > - (*compaction_retries)++;
> > + if (compact_result == COMPACT_SUCCESS) {
> > + /*
> > + * !costly requests are much more important than
> > + * __GFP_RETRY_MAYFAIL costly ones because they are de
> > + * facto nofail and invoke OOM killer to move on while
> > + * costly can fail and users are ready to cope with
> > + * that. 1/4 retries is rather arbitrary but we would
> > + * need much more detailed feedback from compaction to
> > + * make a better decision.
> > + */
> > + if (order > PAGE_ALLOC_COSTLY_ORDER)
> > + max_retries /= 4;
> >
> > - /*
> > - * All zones were scanned completely and still no result. It
> > - * doesn't really make much sense to retry except when the
> > - * failure could be caused by insufficient priority
> > - */
> > - if (compact_result == COMPACT_COMPLETE)
> > - goto check_priority;
> > + ret = ++(*compaction_retries) <= max_retries;
> > + goto out;
>
> I think you simplified this part too much, so now once it runs out of
> retries, it will return false, while previously it would increase the priority.
Oops, I'll send a delta fix to Andrew tomorrow. Thanks!
